Seventeen children and a teacher were burnt to death in Pakistan’s Punjab province on Saturday when the bus taking them to a school caught fire apparently due to a cylinder explosion, local media reported.

Seven children were critically injured in the blaze on the outskirts of Gujrat, 120 miles southeast of Islamabad, DawnNews reported.

The blaze apparently was caused when a faulty gas cylinder in the vehicle exploded resulting in the fire.

“This is a very sad incident. According to our information, at least 17 children were burned to death,” Police officer Mohammed Rasheed told Associated Press. “The school bus caught fire after the blast. We have transported all the victims to a nearby hospital,” he added.

The school bus was carrying more than 20 children to their school, when it suddenly caught fire. The children were between the ages of five and 12, and the female teacher was believed to be in her early 20s, Asif Bilal Lodhi, the top civilian official of Gujrat district told the New York Times.

The bus driver fled the scene and police were conducting raids to arrest him, Reuters reported.

Many vehicles in the energy-starved Pakistan depend on cheap compressed natural gas for fuel. Cylinder blasts are common in the country as fuel is contained in substandard cylinders.